import java.util.*;



public class Main {

    public static void main(String[] args) {
        Person person = new Person();
        System.out.println("123"+ person);

        Main main = new Main();
        main.ref(person);

        System.out.println("789"+person);
    }
    public void ref(Person person) {
        person = null;
        System.out.println("456"+person);
    }
}

class Person{}


//public class Main{
//    public static void main(String[] args) {
//        Box box = new Box(1,2);
//        System.out.println(box);
//        ref(box);
//        System.out.println(box);
//    }
//    public static void ref(Box box) {
////        box = null;
//        box.a = 10;
//        System.out.println(box);
//    }
//}
//class Box{
//    int a;
//    int b;
//
//    public Box(int a, int b) {
//        this.a = a;
//        this.b = b;
//    }
//}